I understand the argumentation behind this, but I don't believe the current vaults need incentivization. Every time the debt limit is increased for the alUSD vault it's usually gone within days; the debt limit for the original alETH vault was reached in like 3 hours. So right now incentivization of the vaults makes little sense because we don't have a demand issue, but rather a supply issue (if you will).
Incentivization of the vaults might help to distribute ALCX to a wider range of users, but I'm not sure if that is a priority at the current stage of the protocol. Might be a good thing to implement this idea at a more mature stage though (as Aave for example did).